When suddenly subjected to high temperature sources, such as flames, galvanic cells of some types may disassemble possibly causing damage to person and property. This possibility of cell disassembly is particularly present in high energy systems such as lithium cells, particularly those employing oxyhalides as cathode/electrolytes wherein the lithium anode is disposed adjacent the cell housing.
One approach to preventing cell disassembly due to external heating would be to surround the cells with a thick layer of insulating material. In some cases this may be an acceptable approach: but for most applications, such as in miniaturized electronic devices, the small battery compartment provided precludes use of bulky cell insulation. What is required is a means for protecting the cells from heat without greatly increasing the bulk of the cells. This is particularly true during shipment of the cells as once the cell has been inserted into a device the device itself will provide some degree of thermal insulation.
Another approach which may be adapted is to provide cells with a safety venting means, such as that shown in U.S. Pat. No. 4,329,405 issued on May 11, 1982. Such venting means rely typically on pressure caused, for example, by the heating of the electrolyte to force open the safety venting means. These venting means will normally provide adequate security against cell disassembly. However, it is believed with regard to certain cell systems that should the anode melt before the electrolyte becomes hot enough for its vapor pressure to reach the venting pressure necessary to operate the cell's venting means a chemical reaction may occur causing the cell to disassemble. Consequently, it would be desirable to ensure that cells provided with such a safety vent could safely vent without disassembly even if subjected to sudden high temperatures.
It is therefore an object of this invention to provide a galvanic cell having an insulating means such that said cell will possess a reduced propensity to disassemble when subjected to sudden elevated temperture, which cell occupies substantially the same volume and contains an equal amount of active materials as conventional galvanic cells.
It is another object of this invention to provide a galvanic cell having a safety venting means and having an insulating means such that when said cell is subjected to sudden high heat the insulating means will enhance the ability of the safety venting means to operate thereby reducing the chance of cell disassembly.
It is a further object of this invention to provide a galvanic cell comprising a lithium anode and an oyhalide cathode/electrolyte, a safety venting means and an insulating means such that when said cell is subjected to sudden high heat the insulating means will delay the melting of the lithium anode until the cathode/electrolyte has boiled, forced open the safety venting means and escaped from the cell, thereby preventing the lithium from chemically reacting with the oxyhalide thus avoiding potential disassembly of the cell.
The foregoing and additional objects will become fully apparent from the following description and the accompanying drawings.